Spatial Light Modulator with Diffractive Correction for LCOS Switching
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Solution Overview
Problem
Existing liquid crystal on silicon (LCOS) spatial light modulators used for wavelength selective switches face challenges in providing spatially varying phase control and beam shaping, which compromises phase availability for switching and fine-tuning individual wavelength channels.
Innovation Solution
A spatial light modulator incorporating a diffractive optical element with sub-wavelength gratings between electrodes, allowing for position-dependent wavefront correction and enhanced reflectivity, which includes a high contrast grating structure composed of high and low refractive index materials to apply a phase profile that corrects optical aberrations and enhances reflectivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If phase modulation is used for wavefront correction in LCOS spatial light modulators, then wavefront correction capability is improved, but phase availability for switching and fine-tuning wavelength channels is reduced
Solution Approach 1:
The spatial light modulator is divided into two independent functional components: a diffractive optical element (DOE) layer dedicated to wavefront correction and an LCOS layer dedicated to switching and modulation. This segmentation allows each component to perform its specific function without interfering with the other, thereby resolving the contradiction between wavefront correction capability and phase availability for switching.
Solution Approach 2:
A separate diffractive optical element layer is introduced as an intermediary component between the incident light and the LCOS layer. This intermediary handles the wavefront correction function, allowing the LCOS layer to focus exclusively on switching operations, thus maintaining both wavefront correction capability and phase availability for switching.
2Illumination intensity
If sub-wavelength grating structures are incorporated to enhance reflectivity, then reflectivity is improved, but spatially varying phase control capability is lost
Solution Approach 1:
The device is segmented into distinct functional layers: the diffractive optical element layer provides spatially varying phase control through its patterned structure, while the separate reflective layer (with or without sub-wavelength gratings) provides enhanced reflectivity. This segmentation allows both spatially varying phase control and enhanced reflectivity to coexist without compromising either function.
Solution Approach 2:
The spatial light modulator employs a composite structure combining different functional layers: a diffractive optical element layer with sub-wavelength features for phase control, a liquid crystal layer for modulation, and a reflective layer with sub-wavelength grating structures for enhanced reflectivity. This composite architecture enables simultaneous achievement of spatially varying phase control and high reflectivity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution provides effective wavefront correction and beam steering while maintaining sufficient phase for switching, improving the performance of wavelength selective switches by optimizing phase distribution and enhancing reflectivity.
Implementation Method 1
The diffractive optical element has an array of diffracting formations formed from sub-wavelength structures. The array of diffracting formations defines a phase profile adapted to modify the incident wavefront of light reflected off the second electrode and to apply a position-dependent wavefront correction to the reflected wavefront of light.
Implementation Method 2
The diffractive formations are formed of a first material having a high refractive index that is surrounded by one or more second materials having a lower refractive index than the first material.
Implementation Method 3
The first and second electrodes are disposed on opposing sides of the liquid crystal material and are connected to an electric circuit for applying an electric potential across the liquid crystal material.
Implementation Method 4
The second electrode is reflective and divided into a two-dimensional array of independently electrically controllable pixels
Data Source
AI summary
A spatial light modulator (100) comprises a liquid crystal material (104), first and second electrodes (106, 108) disposed on opposing sides of the liquid crystal material (104), and a diffractive optical element (120) disposed between the electrodes (106, 108) and extending laterally across the modulator (100). The diffractive optical element (120) comprises an array of diffracting formations (122) formed from sub-wavelength structures. The array of diffracting formations (122) defines a phase profile adapted to modify the incident wavefront of light reflected off the second electrode and to apply a position-dependent wavefront correction to the incident wavefront of light.